One of the major emphases of this proposed work is to understand the importance of the tissue interactions that occur during early embryonic development. The particular tissues under primary study are the embryonic notochord and adjacent somites. In vivo and in vitro studies have shown that the embryonic notochords stimulates the somitic mesenchyme to undergo chondrogenesis. The notochord synthesizes both proteoglycans and collagen Type II, the molecules characteristic of cartilage matrix. We have shown that exogenous proteoglycans and exogenous collagen (Type I, II, and III) are capable of stimulating somite chondrogenesis. We plan to use different ionic concentrations of the extracting salt guanidinium hydrochloride to take apart the proteoglycan molecule, to see if there is a particular portion of the molecule that is the effective stimulator. We will also do size distribution profiles to see if a particular type of proteoglycan is correlated with the onset of chondrogenesis. Further studies using enzymatic digestion to remove the glycosaminoglycans from the monomeric proteoglycan will enable us to test smaller portions of the molecule. Correlated with these studies on RNA synthesis and morphological studies utilizing the scanning electron microscope. BIBLIOGRAPHIC REFERENCES: Vasan, N.S. and J.W. Lash 1976 Chondrocyte metabolism as affected by Vitamin A. Calc. Tissue Res. 19: 99-107. Lash, J.W. 1976 Extracellular matrix products and differentiation: Somite chondrogenesis. (Symposium on Teratogenesis) Institut de la Vie. North Holland, Amsterdam, pp. 367-373 (in press).